Decorative cementitious panel and method of manufacture

ABSTRACT

UNCURED, CEMENITIOUS SHEETS ARE EXPOSED TO PARTICLE BLASTING UNDER CONDITIONS WHICH RESULT IN THE PARTICLES ADHERING TO THE CEMENTITIOUS MATERIAL AND PROJECTING ABOVE THE SURFACE OF THE SHEET.

Aug. 29, 1972 A. SCHEPPERS 3,687,800

DECORATIVE csnau'rnzovs mum. AND METHOD 0? murm'wu Original Filed Sept. 16. 1971 United States Patent Oflice 3,687,800 Patented Aug. 29, 1972 ABSTRACT OF THE DISCLOSURE Uncured, cementitious sheets are exposed to particle blasting under conditions which result in the particles adhering to the cementitious material and projecting above the surface of the sheet.

This application is a continuation of US. application Ser. No. 668,119, filed Sept. 15, 196-7 and now abandoned.

BACKGROUND OF THE INVENTION An important consideration in the construction of new oflice buildings, apartment buildings and similar structtures, and in the renovation of old buildings, is the type of facing material to be used as the outer veneer surface. A popular choice has ben natural stone panels and precast concrete panels of relatively great thickness which provide a natural rugged appearance architects often favor. The initial cost of such materials and the expense and trouble of installing them, due to their great weight, has led to a search for different types of materials which, when installed, suggest these same characteristics, but which are not as expensive and are easier to install.

One type of panel which is relatively inexpensive to manufacture and can be readily handled and installed by workmen is a relatively thin preformed asbestoscement panel. Although its thickness may be only about inch, such a panel when installed gives an overall impression of massiveness due to its resemblance to natural stone and thick precast concrete panels. This impression is heightened when the panel is provided with ribs on its exterior surface, such ribs being formed by molding or, preferably, by extruding.

One of the problems associated with this type of product and with other cementitious products is the appearance of bloom on the surface of the panel. Bloom is caused by the leaching out of calcium carbonate from the cementitious composition during the curing of the panel, which produces an undesirable 'white b-lotchy appearance. In addition, due to the nature of the product and the curing operation, the color sometimes varies even within a single panel creating an undesirable elfect. Bloom can be removed by sand blasting the exterior surface of the panel after it has been cured, thereby producing a roughened surface which generally is pleasing in appearance because it breaks up the otherwise smooth expanse of the surface. While such a surface can make color variations less noticeable, it does not solve this problem. Further, sand blasting is a lengthy and expensive operation, and often the texture produced by sand blasting is not deep enough or rough enough to show at any substantial distance from the panel. A better method of producing an acceptable surface on a cementitious panel would be highly desirable, particularly one which can produce such a texture on the portions of a panel face between ribs or other relatively large surface projections.

OBJECTS OF THE INVENTION The main object of the invention is to provide a cementitious panel having a surface texture which hides any bloom which might be otherwise on the surface, conceals color variations in the cementitious material, and provides a surface finish which is highly pleasing in appearance.

Another object of the invention is to produce such a panel in an economical and simple manner.

SUMMARY OF THE INVENTION The problems discussed above are overcome by the present invention which provides a cementitious panel having particulate material generally uniformly distributed over a substantial portion of the panel surface. This arrangement conceals any bloom or color variation in the panel and in addition provides a highly pleasing surface texture. Surprisingly, it has been found that particles can be made to project above the surface of a panel a greater distance than they extend below the surface into the panel body, and yet adhere to the panel under adverse freeze-thaw conditions which normally would be expected to dislodge them.

Particles can be made to adhere to the panel in this manner while the panel is still uncured. This is accomplished by hurling particulate material against the surface of the panel when the cementitious material at the surface is in a plastic condition such that it can be displaced and yet hold such displaced shape. The particles are hurled with sufficient force to cause a portion of most particles to become embedded in the cementitious material, but not with sufllcient force to cause the entire particle, or substantially the entire particle, to become embedded. A substantial portion of the particle remains above the panel surface. The particle is held in place not only by the bond between the bottom portion of the particle and the cementitious material, which normally would not be sufficient to securely bond the particles in place against the rigors of weathering and handling, but also by a thin layer of cementitious material connecting the projecting portion of the particle to the cementitious material of the panel surface. Such thin layers of cementitious material are produced by the splatter of uncured cementitious material which occurs when a particle strikes the surface of a panel with sufiicient force. It is not necessary to completely cover the entire surface of the panel with particulate material in order to achieve the desired appearance. The cementitious material itself can show through the spaces between particles without creating an undesirable appearance, but it is preferred that the spaces be rather small so that color variation and bloom are not noticable. Subsequent curing of the cementitious material bonds the particles securely to the panel substrate.

DESCRIPTION OF THE DRAWINGS The nature of the invention will be more fully understood and other objects may become apparent when the following detailed description is considered in connection with the accompanying drawing wherein:

FIG. 1 is a pictorial representation of a typical panel incorporating the present invention;

FIG. 2 is a side end view of the panel shown in FIG. 1;

FIG. 3 is a view similar to that of FIG. 2 but showing a panel having a modified cross-sectional configuration;

FIG. 4 is a diagrammatic representation of a process for producing the particulate covered cementitious panel of the present invention;

FIG. 5 is a sectional view taken on line 5-5 of FIG.

FIG. 6 is an enlarged sectional view taken through a portion of a prior art panel;

FIG. 7 is an enlarged partial plan view of a corner of a panel having particulate material embedded in the surface thereof in accordance with the present invention; and

FIG. 8 is an enlarged sectional view taken on line 88 of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2, a typical example of a panel illustrating the surface finish of the present invention is indicated at 10. The surface 12, adapted to be exposed to view when the panel is installed on a building wall, has a large number of particles 14 adhered to it and distributed over it in a generally uniform arrangement.

As shown in FIG. 3, the panel need not have a fiat surface. The panel 16 of FIG. 3 has an outer surface 18 which includes a number of spaced ribs 20 projecting above the surface 18 and extending the length of the panel. In this arrangement the particles 22 are adhered to the outer surfaces of both the ribs 20 and the portions of the exterior surface 18 between the ribs.

A preferred method for adhering the particulate material to the surface of the panel is illustrated in FIGS. 4 and S. The ingredients of the cementitious mixture are blended together in a mechanical mixer 24 and then transported to an extruder 26. The shaped cementitious sheet 28 formed of unitary, substantially homogeneous construction by the extruder is supported as it leaves the extruder die by a continuous conveyor belt 30 trained around pulley 32. Intermediate the ends of the conveyor is a particle blasting device 33 which, in the typical embodiment shown, comprises a tank 35 of compressed air having a flexible hose 36 extending therefrom. A nozzle 38 is attached to the end of the hose 36 and is slidably mounted between spaced tracks 40 supported by posts 42. The nozzle is connected, as by a pin, to the piston rod 44 of a suitable air cylinder 46. As the air cylinder reciprocates the piston rod 44, the nozzle 38 moves from side to side over the conveyor and sprays the particulate material 50 onto the upper surface of the sheet 28. Suitable switches and circuitry can be provided to cause the air cylinder to reverse the direction of movement of the piston rod 44 when the nozzle has reached its limit of travel in either direction.

The condition of the cementitious material at the upper surface of the sheet 28 at the time the particles are hurled toward it should be such that the material is displaced by the particles as they strike the surface, and is splattered somewhat by their impact, but the material should not be so plastic that it is unable to hold its shape after the displacement of material occurs. It is not practical to attempt to define this condition by placing limitations on the numerical values of certain properties of the material, since there are too many factors affecting the ability of the material to be displaced and yet hold its displaced shape. For example, although the amount of water in the composition affects its consistency and thus its shapeholding ability, there is no minimum or maximum amount of water that is critical to the success of the process regardless of the specific cementitious composition used.

The amount of water necessary to make one particular composition of the proper consistency and plasticity may be too little or too much for another composition. The presence of asbestos fibers, for example, will give the composition a greater capacity to retain water without becoming too plastic for proper shaping. In addition, fillers or additives, such as modifiers for facilitating extrusion of the material, are capable of affecting the consistency of a cementitious composition. An example of the condition of an uncured cementitious product suitable for use in the process of the invention is that of the surface of an extruded asbestos-cement shape as it leaves the extruder, and for a short time thereafter, wherein the uncured asbestos-cement is capable of holding its shape, even though it includes a surface of non-planar configuration.

As indicated above, the composition of the cementitious sheet may vary. It is preferred that it be comprised of abestos-cement because asbestos fibers provide the finished cured product with sutficient strength to permit the product to be made as thin as possible, a typical thickness being of the order of inch, and they also assist in providing the uncured product with enough strength to retain its shape until it is cured. Preferred percentage ranges of ingredients by weight, for the base sheet of a product to be covered with particulate material according to this invention are as follows:

Percent Hydraulic cement 10-85 Asbestos 1-60 Auxiliary cementing agent (e.g., silica) up to 55 Water 14-50 Filler material up to 25 Modifying agent to assist in extruding up to 10 Any suitable type of hard granule may be used as the particulate material, the selection of which depends on the desired appearance of the product. Typical examples of suitable particulate material are sand, quartz, marble and limestone. It is impractical to assign any limitations to the size of the particles or to the speed of the particles at the time they contact the surface of the cemenitious sheet since the particle size and speed may vary considerably depending upon the cementitious material used and its consistency. Generally, the smaller the particle, the greater its velocity should be at the time of contact, and the larger the particle, the less velocity it need have at the time of contact. Particle sizes in the general range of 16 mesh to 70 mesh are preferred because of cost, handling and appearance considerations, particularly particles in the range of 20 mesh to 50 mesh.

The granules need not be hurled by means of a particle blasting apparatus, but may be given the desired velocity by any other suitable mechanical arrangement. A rotary wheel or belt, for example, which carries the particles to a certain point and then flings them by centrifugal force against the product could be used. Particle blasting apparatus is preferred, however, because it is simple to use and because the particles are uniformly spread and their velocity easily varied. An example of a suitable arrangement utilizing a particle blasting apparatus in connection with particles generally in the size range of 16 mesh to 70 mesh is to space the nozzle of the particle blaster 2 to 3 feet above the surface of the cementitious sheet and to spray the particles under pressure of from 20 p.s.i. to 60 p.s.i. The actual pressure which will produce the best results will vary according to the particle size, the distance the nozzle is spaced from the sheet and according to the diameter of the nozzle. With a @5 inch nozzle spaced about 2 /2 feet from the sheet, it has been found that a pressure of about 20 to 35 p.s.i. produces best results.

The granules need not approach the sheet at exactly right angles, but can be hurled at angles considerably less than This permits the granules to be adhered to surfaces of the sheet which extend vertically from the upper surface when the sheet is supported by a moving conveyor, such as the side walls of projecting rib portions. Such surfaces ordinarily would not be contacted by particles hurled at the sheet at right angles thereto.

The manner in which particles are adhered to the surface of the cementitious base by this invention is in contrast to the prior art practice of embedding granules in the surface of an asbestos-cement roofing shingle by means of roller pressure. Referring to FIG. 6, which shows an enlarged portion of a product of this type, the granules 52 are embedded in sheet 54 to such an extent that only a small portion of their height is exposed to view. Since the granules are irregular in shape, this arrangement permits the widest portions of the granules to be beneath the surface, thus enabling such portions to be completely covered by the cementitious material to mechanically hold the particles in place. The material in the areas overlying projecting portions 62, 64 and 66 of the granules 52 illustrates this feature. This type of arrangement is undesirable for the decorative sheet of this invention because it does not provide enough of an ap pearance of surface texture and also because it would be highly impractical, if not impossible, to utilize roller pressure to embed granules in a very thin green cementitious sheet that has just been extruded and must hold its extruded shape until cured. This is of particular importance where the extruded sheet has a non-planar crosssectional surface, such as for example, a ribbed configuration as shown in FIG. 3. The high roller pressure required to embed the granules in the manner shown in FIG. 6 would tend to deform and perhaps crush the ribs 20 of the sheet of FIG. 3. Further, a roller, normally could contact only the upper surfaces of the ribs, not the valley portions between the ribs.

As illustrated in FIGS. 7 and 8, the particles 50 adhered to sheet 28 extend a substantial distance above the surface of the sheet. The surface of the granules in contact with the cementitious material in the craters formed by the granules as they strike the sheet are bonded to the cementitious material by the curing of the cement. As shown in FIG. 8, however, this is a relatively small area, compared with the surface area of the granules, and in most cases the widest part of the granules will still be above the surface of the sheet, thereby minimizing the ability of the cement in the crater portion to mechanically hold the granules in place. This is compensated for by the surprising effect of the cementitious material that is displaced and splattered as a result of the impact of the particles. Microscopic examination of sheets prepared in accordance with this invention reveals that the splattered material is randomly distributed over the particles in very thin small areas which cover various parts of the particles. Enough of the material is splattered, however, so that most granules are covered by one or more patches of cementitious material in the form of a thin layer connect ing both the surface of the sheet and the side of the granule. This arrangement is illustrated in FIGS. 7 and 8 by the thin layers of cementitious material 70 and 72' contacting granule 50a and the thin layer 74 contacting the granule 50b. Since these thin layers contact both the surface of the sheet 28 and the sides of the granules 50a and 50b, they act as a mechanical bond to hold the granules in place and to assist the bond between the granules and the cement at the crater portion.

Ordinarily, it would be expected that particles adhered to a cementitious base such that they project a considerable distance from the base to form a rough surface would be susceptible to freeze-thaw conditions, and that repeated freezing and melting of water between the particles and in minute cracks and crevasses at the base of the projecting portions of the particles eventually would cause the particles to be loosened and dislodged from the base. Panels constructed in accordance with the present invention, however, did not behave in this manner. Asbestos-cement panels were extruded, and within a few minutes after leaving the extruder, were sprayed with sand particles predominantly of from 20 to 40 mesh size. The particle blasting apparatus was spaced a distance of 30 inches from the face of the panels and the air pressure, used in connection with a 1 inch nozzle opening, was about 30 psi. The panels were covered with a generally uniform distribution of particles spaced apart only slightly.

The panels were subjected to three separate tests. One panel was soaked in water for about 8 hours, then placed on edge in a freezer at a temperature of about 0' F. for a period of at least 16 hours. Fifty cycles of such alternate soaking and freezing were carried out.

Another panel was subjected to fifty cycles of alternate freezing and thawing, wherein each cycle consisted of subjecting the panel to a temperature of about 0 F. for a period of at least 16 hours and then exposing it to room temperature for about 8 hours.

In the third test, a panel was sprayed with water in an environment having a temperature of about 0 F. and was allowed to remain, standing on edge, at this temperature for at least 16 hours. It was then exposed to room temperatures for about 8 hours. Fifty cycles of such alternate freezing and thawing were carried out.

In each case, the severe conditions to which the panels were exposed loosened only a few granules. The adhesion of all other granules remained secure and the appearance of the panel was the same as before the tests were run. In view of the great number of sand particles on the panel face, the loosening of only a few was a remarkable performance.

In summary, this invention permits particulate material to be adhered permanently to the face of a cementitious sheet even though the greater part of a particle extends above the surface of the sheet. This is made possible by the bonds established by the thin layers of cementitious material displaced from the cementitious base by the impact of the particles. This permits an unusually rough surface to be provided which is highly desirable from an architectural point of view. The invention also permits particles to be provided on shaped cementitious products which are not adapted to be contacted by mechanical pressure devices such as rollers. The generally uniform covering of particles also hides any deposits of bloom and conceals variations in color which might otherwise be apparent.

What I claim is:

l. A cementitious panel adapted for use as an exterior building panel, which comprises:

(a) an extruded base of unitary, substantially homogeneous, construction comprising hydraulic cement and having a surface adapted to be exposed to view;

(b) particulate material generally uniformly distributed over a substantial portion of said surface of said extruded base;

(c) most of the individual particles of the particulate material being partially embedded in and adhered to the extruded, cementitious base material and extending into the base a distance substantially less than the thickness of the base;

(d) a substantial number of particles projecting above the surface a greater distance than the distance to which the particles are embedded in the base;

(e) the thickness of said base plus an above-surface projection of said partially embedded particles measuring, in summation, the thickness dimension of said panel for a given location; and

(f) relatively thin layers of cementitious material engaging the projecting portions of said particles and being connected to the base to assist the cementitious material contacting the embedded portions of such particles in bonding such particles to the base.

2. A cementitious material as recited in claim 1, wherein the surface adapted to be exposed to view is non-planar.

8 3. A cementitious material as recited in claim 1, wheretitious material is comprised of asbestos-cement. in the cementitious composition is comprised of asbestos 6. A method as recited in claim 4, wherein the particles cement. are hurled at the base by air pressure.

4. A process for producing a decorative surface on a cementitious article, comprising the steps of: References Cited (at) extruding an uncured cementitious base of unitary, UNITED STATES PATENTS substantially homogeneous construction having a surface adapted to be exposed to view; 1 g; fil a i (b) the cementitious material at the surface being in 9/1924 6 2 1 X a plastic condition shortly after extrusion to the ex- 333117s 7/1967 i 5 3 5 X tent that such material can be displaced and can sub- 3390496 7/1968 f i SL315 sequently hold such displaced shape; 8 12/1924 'i at a 5 1 X (c) hurling particulate material at the surface shortly l893'783 1/1933 l after the base has been extruded with suflicient force 2096242 10/1937 z 161-462 to cause most of the particles to extend into the base 15 2s73659 10/19 1 Bar b Isl-205 a distance substantially less than the thickness of the 3, g Bollaert Q base, to become partially embedded therein, and to 2/195: Smfflak et a1 161-205 splatter thin layers of such material onto portions Smith 161-205 of particles projecting above the surface; 7/1954 at 161-205 (d) the thin layers of cementitious material being con- 20 named to the Surface, and IOHN T. GOOLKASIAN, Primary Examiner (e) the particulate material being generally uniformly G. W. MOXON II, Assistant Examiner distributed over a substantial portion of the surface, and US. Cl. X.R.

(f) curing the cementitious material. 5 3 5; 7 5;1 1 154 15 205 5. A process as recited in claim 4, wherein the cemen- 

